1. Field of the Invention
The present invention relates to a mounting structure for semiconductor devices such as power MOSFETs and a feeding-side charger comprising the semiconductor device mounting structure.
2. Description of the Prior Art
A conventional electromagnetic induction system feeding-side charger, such as one used to charge a battery of an electric automobile, comprises a power circuit board having formed therein a power conversion circuit for converting a commercial alternating current to a high-voltage high-frequency alternating current. The power conversion circuit comprises, for example, a rectification/power factor improving circuit and a resonance converter. The resonance converter is constituted by four (4) or eight (8) bridge connected power MOSFETs.
As is known, MOSFETs generate much heat when they are in operation. Therefore the MOSFETs are mounted on a heat radiating unit fixed on a circuit board. The heat radiating unit is made of, for example, an aluminum alloy and is provided with heat radiating fins for radiating heat, transferred from the MOSFETS, to the atmosphere. The radiating unit continues to cool the MOSFETs by radiating heat transferred from the MOSFETs to the atmosphere. In order to secure a sufficient heat radiating capacity from heat radiating fins, the mounting area of a heat radiating unit is designed to be remarkably larger than the mounting area of the MOSFET main bodies.
On the other hand, since smaller feeding-side chargers have been demanded, there is now a demand for smaller power circuit boards which govern the size of a feeding-side charger. This has triggered a demand for the reduction in mounting area of the heat radiating unit of MOSFETs whose mounting area occupies a large portion on a circuit board.
However, when a heat radiating unit having a smaller mounting area is used, the MOSFETs mounted thereon cannot be cooled sufficiently, and the mounting density of the MOSFETs cannot be increased. Due to this, the mounting area of the power MOSFETs cannot be reduced. These problems apply not only to a case where a plurality of MOSFETs are mounted but also to a case where a single power semiconductor device is mounted.
The present invention was made with a view to solving the above problems and the object thereof is to provide a semiconductor device mounting structure which can improve the cooling efficiency of semiconductor devices, relative to the mounting area thereof on a circuit board, so as to increase the mounting density of semiconductor devices, and a feeding-side charger provided with the same mounting structure of a semiconductor device.
With a view to solving the above problems, according to a first aspect of the present invention, there is provided a semiconductor device mounting structure wherein a heat transfer unit, which comes into contact with a heat radiating unit installed contiguously with the circuit board, is fixed to a circuit board on which semiconductor devices are mounted, and wherein the main bodies of the semiconductor devices mounted on the circuit board come into contact with the heat transfer unit.
According to the first aspect of the present invention, heat generated in the main bodies of the semiconductor devices when they are put in operation is transferred to the heat transfer unit, with which the main bodies of the semiconductor devices come into contact, and is then transferred therefrom to the heat radiating unit for radiation therefrom. Thus, when compared with the conventional mounting structure, in which heat from semiconductor devices is radiated by a heat radiating unit directly connected on a circuit board, since heat from semiconductor devices according to the mounting structure of the present invention is radiated by the heat radiating unit having a great heat radiating capacity, which can be provided irrespective of the mounting area on a circuit board, the heat radiating capacity per mounting area for mounting the heat transfer unit replacing the conventional heat radiating unit, on a circuit board, can be increased.
The present invention may be more fully understood from the description of the preferred embodiments of the invention, which will be described below, together with the accompanying drawings.